1. Field of the Invention
The present invention relates to an image formation apparatus which has a plurality of developing units, and develops a latent image formed on an image carrier to obtain a toner image and sequentially transfers and overlaps toner images on a transfer material to obtain a desired image.
2. Related Background Art
In a conventional image formation apparatus, a transfer material is supported on a drum-like transfer material supporting member, and toner images formed on an image carrier can be multiple-transferred a plurality of times to a single transfer material.
For example, in a color image formation apparatus, yellow(Y), magenta(M), cyan(C), and black(BK) developing units are arranged, and the transfer material support member is rotated four times so as to transfer toner images of four colors, e.g., yellow, magenta, cyan, and black images since a toner image of one color on an image carrier is transferred per rotation of the transfer material support member.
However, after an image of one color is transferred per rotation of the support member, an image formation process for the next color is not yet completed upon the next rotation depending on the size of the transfer material. Therefore, the support member is rotated once more, and a transfer operation for the next color is performed upon the second next rotation. More specifically, the transfer drum is subjected to a rotation for the transfer process and an extra rotation. Therefore, in order to complete the transfer processes for the four colors, at least three extra rotations are necessary.
During the extra rotation without the transfer process, since the toner image which has been already transferred onto the transfer material is again in contact with the surface of the image carrier, toner is offset from the toner image on the transfer material onto the surface of the image carrier due to this contact, thus blurring the transferred image.